1. Field of the Invention
The present invention concerns an optical rotary encoder adapted to intermittently shut an optical path of a photointerruptor by the rotation of a rotatable pulse scale and generate and detect optical pulse signals in accordance with an angle of rotation of the pulse scale and, more in particular, it relates to an optical rotary encoder which can be suitably used in severe working circumstances giving undesired effects of electromagnetic noises or vibrations or in a restricted space, for example, a rotary encoder used as a crank angle sensor in a car engine.
2. Description of the Prior Art
Known rotary encoders include those comprising a optical device type photointerruptor using a pair of a light-emitting device and a light-receiving device and an optical fiber type photointerruptor using a pair of a light-emitting optical fiber and a light-receiving optical fiber, as means for detecting optical pulse signals.
The optical rotary encoder of the optical device type photointerrupter comprises a light-emitting device and a light-receiving device disposed on both sides of a coded pattern formed on a pulse scale.
Light from the light-emitting device is irradiated to the pulse scale and optical pulse signals are generated when the optical path of the light is shut intermittenty by the coded pattern upon rotation of the pulse scale, and converted by the light-receiving device into electric signals.
However, when such an optical rotary encoder is used, as for example, a car engine, erroneous operation is caused by electromagnetic noises, etc., making it impossible for accurate pulse detection.
The optical rotary encoder using the optical fiber type photointerruptor includes a transmission type in which ends of a light-emitting optical fiber and a light-receiving optical fiber are opposed to each other on both sides of the pulse scale, and a reflection type in which a light-emitting optical fiber and a light-receiving optical fiber are disposed on one identical side of a pulse scale on which a coded pattern is formed.
The optical fiber type photointerruptor is free from erroneous operation caused by the electromagnetic noises, etc. since detected signals are transmitted in the form of optical signals.
However, in order to minimize the loss of optical transmission, a micro-lens such as a rod lens has to be attached to the top end of each optical fiber. Then, accurate alignment is necessary for the optical axes between the optical fiber and the rod lens attached thereto. Such alignment is necessary between the light-emitting and light-receiving optical fibers as well.
Further, the number of additional parts such as rod lenses and the number of assembling steps are increased to require much production cost.
Further, in the transmission type optical rotary encoder, wiring operation for the light-receiving and light-emitting optical fibers disposed on both sides of the pulse scale is troublesome. In addition, since a quartz type optical fiber used for reducing the optical transmission loss can not be bent with an acute angle, it brings about a difficulty in installing the optical fibers in a restricted space.
Meanwhile, in the reflection type optical rotary encoder, the wiring operation for the light transmitting and receiving optical fibers is relatively easy, but it often causes misalignment for the reflected light upon irregular vibrations of a pulse scale making accurate measurement difficult or even impossible.